Reading/Deleting Last Line Of File
jim at visitrieve.com
Thu Feb 11 18:11:15 CST 2010
Alex Tweedly wrote:
> Jeff Massung wrote:
> > Warren,
> > I've read through most of these suggestions, but I'm surprised that
> > obvious hasn't been suggested yet (that I've seen): skip
> Hasn't been suggested because it won't work.
> > put the length of url "file:myfile.txt" into tEnd
> > open file "myfile.txt" for text update
> > seek to tEnd in file "myfile.txt"
> > >From here just back up a "reasonable" number of characters... say
> 200. Find
> > the last CR character, nuke everything else and close the file.
> Didn't find
> > one? Try backing up another 200, etc. It'll be a whole lot faster.
> "... nuke everything else ...." ?? How ?
> You've opened the file for update, so anything that you write to the
> file *overwrites* any existing characters at the same position(s), and
> leaves everything following that unchanged. So there is no way to
> shorten a file if opened in update mode.
> I *think* the best you can do is
> 1. find file length (best to use the detailed files)
> 2. open for read, and read some chunk at the end (200, 1000, whatever
> (open for read is more efficient than open for update)
> 3. calculate the number of bytes to be deleted off the end of the file
> 4. close the file
> 5. open the file for append
> 6. write empty to the file at the appropriate point
> > Edge case to concern yourself with would be if your file happens to
> end with
> > a CR and maybe you want to ignore those cases. But that should be
> > enough to solve.
> Easiest (and I think best) way to resolve that corner case is to
> preserve the trailing CR if it's there to begin with, and not leave one
> if it wasn't there to start with. This happens to involve no extra work
> at all, hence it's the easiest one :-)
> I decided it was time to email some (reasonably tested) revTalk rather
> than just ideas ....
> (NB assumes that the defaultfolder has already been set to the
> appropriate place)
> > on deletelastline pFile
> > constant K = 1000
> > put the detailed files into t
> > filter t with pFile & ",*"
> > put item 2 of t into tFileLength
> > open file pFile for read
> > seek to tFileLength-K in file pFile
> > read from file pFile until end
> > close file pFile
> > put the number of chars in the last line of it into tNum
> > open file pFile for append
> > write empty to file pFile at (tFileLength-tNum-3)
> > close file pFile
> > end deletelastline
> -- Alex.
Just one thing Alex, you need to:
put URLDecode(the detailed files) into t
in case the file name has, for example, a space in it.
Aloha from Hawaii,
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